1. Field of the Invention
The present invention relates in general to a fluid-filled cylindrical elastic mount, and more particularly to such a fluid-filled cylindrical elastic mount which is capable of exhibiting damping effect with respect to input vibrations applied in its axial direction, based on flows of a fluid contained therein and which may be suitably used as a member mount for a suspension system of a motor vehicle, for example.
2. Discussion of Related Art
As one type of a mounting device interposed between two members in a vibration system to connect these two members in a vibration-damping fashion, there is known a so-called fluid-filled cylindrical elastic mount arranged to exhibit an excellent vibration damping characteristic on the basis of flows (such as resonance) of a fluid contained therein. Such a fluid-filled cylindrical elastic mount is disclosed in JP-A-11-153180, for instance.
Such a conventional fluid-filled cylindrical elastic mount includes, for instance: a center shaft member to be attached to one of the two members in the vibration system; an intermediate sleeve disposed radially outwardly of the center shaft member with a suitable distance therebetween; an elastic body disposed between the center shaft member and the intermediate sleeve for elastic connection therebetween; and an outer cylindrical member which is to be attached to the other of the two members and which is inserted on and fixed to an outer circumferential surface of the intermediate sleeve via a thin sealing rubber layer formed on an inner circumferential surface of the outer cylindrical member.
In the fluid-filled cylindrical elastic mount described above, the elastic body has pockets which are open in an outer circumferential surface thereof. With the outer cylindrical member inserted or fitted on the intermediate sleeve, the outer cylindrical member closes openings of these pockets, so that fluid chambers are formed between the outer cylindrical member and the center shaft member. Each fluid chamber is filled with a non-compressible fluid and is at least partially defined by the elastic body and the sealing rubber layer. Further, in the disclosed elastic mount, an outer flange is formed at one end of the intermediate sleeve located on the side of one of opposite axial ends of the elastic mount along a periphery of an opening of the intermediate sleeve at the above-indicated one end. The outward flange constitutes a stopper mechanism which limits an amount of relative axial displacement between (a) the intermediate sleeve and the outer cylindrical member inserted on the intermediate sleeve and (b) the center shaft member, with the outer cylindrical member and the center shaft member attached respectively to the two members in the vibration system. The thus constructed fluid-filled cylindrical elastic mount is used as a suspension member mount, a strut bar cushion, or a suspension upper support for a motor vehicle, for instance.
In the fluid-filled cylindrical elastic mount constructed as described above, there is formed, at the one end of the intermediate sleeve where the outward flange is formed, a concave portion that is concaved in a radially inward direction perpendicular to an axial direction of the elastic mount. Further, there is formed, at one end of the outer cylindrical member where an outward flange is formed, an engaging portion that is bent in the radially inward direction. The engaging portion of the outer cylindrical member is brought into engagement with the concave portion of the intermediate sleeve with the sealing rubber layer interposed therebetween, thereby assuring a sufficiently high degree of counter force with respect to extracting force that acts on the outer cylindrical member and the intermediate sleeve to cause the outer cylindrical member and the intermediate sleeve to be extracted from each other in the axial direction, that is, extraction-resisting force which resists the extraction of the outer cylindrical member and the intermediate sleeve relative from each other in the axial direction.
In the conventional cylindrical elastic mount described above, with the outer cylindrical member fitted on the intermediate sleeve, the outer cylindrical member is subjected to a diameter-reducing operation such as drawing using eight drawing dies, for instance, so that the outer cylindrical member is fixed to the intermediate sleeve. In this instance, the engaging portion is formed on the outer cylindrical member simply by performing the diameter-reducing operation such that the one end of the outer cylindrical member at which the outward flange is formed has a diameter reduced by an amount larger than an amount of reduction of a diameter of the rest of the outer cylindrical member. At the same time, the force acting on the outer cylindrical member to reduce its diameter (hereinafter, this force may be referred to as “the diameter-reducing force”) acts also on the intermediate sleeve, so that the concave portion is formed, owing to the diameter-reducing force, at the above-indicated one end of the intermediate sleeve at which the outward flange is formed.
Accordingly, the conventional fluid-filled cylindrical elastic mount described above realizes, with excellent manufacturing efficiency and reduced manufacturing cost, a structure that sufficiently assures the extraction-resisting force that resists the extraction of the outer cylindrical member and the intermediate sleeve from each other in the axial direction, without requiring any special equipment or additional procedure.
The inventors of the present invention have made an extensive study on the fluid-filled cylindrical elastic mount constructed as described above for improving the manufacturing efficiency and attaining further reduction in the manufacturing cost of the elastic mount, and have found the following: In the conventional cylindrical elastic mount constructed as described above in which both of the intermediate sleeve and the outer cylindrical member are formed with the respective outward flanges, the formation of the outward flange on the intermediate sleeve and the formation of the outward flange on the outer cylindrical sleeve need to be performed separately in respective different steps, thereby giving an obstacle to the improvement in the manufacturing efficiency and the reduction in the manufacturing cost of the elastic mount.
Further, in the conventional fluid-filled cylindrical elastic mount, the sealing rubber layer is interposed between the concave portion of the intermediate sleeve and the engaging portion of the outer cylindrical member. Accordingly, when the concave portion and the engaging portion are formed on the intermediate sleeve and the outer cylindrical member, respectively, simultaneously upon performing the diameter-reducing operation on the outer cylindrical member fitted on the intermediate sleeve, a part of the sealing rubber member, which part is located between a portion of the outer cylindrical member at which the engaging portion is to be formed and a portion of the intermediate sleeve at which the concave portion is to be formed, is elastically deformed, thereby inevitably absorbing or decreasing the diameter-reducing force to be transmitted from the outer cylindrical member to the intermediate sleeve. Where the amount of absorption of decrease of the diameter-reducing force is excessively large, the configuration of the concave portion formed on the intermediate sleeve may largely differ from the configuration of the engaging portion formed on the outer cylindrical member, resulting in insufficient engagement of the engaging portion with respect to the concave portion. Consequently, there may be caused a risk of reduction in the extraction-resisting force which resists the extraction of the intermediate sleeve and the outer cylindrical member from each other in the axial direction.
To avoid the drawback described above, it may be considered to perform the diameter-reducing operation on the outer cylindrical member with larger diameter-reducing force. The increase in the diameter-reducing force to be applied to the outer cylindrical member, however, leads to an increase in a size of the equipment for performing the diameter-reducing operation, undesirably pushing up equipment cost.
It may be further considered that an intermediate sleeve having the concave portion which has been formed in advance is used and only the engaging portion is formed on the outer cylindrical member by the diameter-reducing operation. Where such an intermediate sleeve is used, however, there may be formed a minute clearance between an inner circumferential surface of the portion of the sealing rubber layer located radially inwardly of the engaging portion of the outer cylindrical member and an inner circumferential surface of the concave portion of the intermediate sleeve, due to deformation of the outer cylindrical member back toward a direction to increase its diameter that inevitably occurs after the outer cylindrical member has been freed from the diameter-reducing force. Such a minute clearance may deteriorate sealing between the outer cylindrical member and the intermediate sleeve.